Humidity, warm nights, shade trees and months of pine pollen make Alabama ideal for mildew, algae and moss. The green film on the north side of a house, the black streaks down a roof and the slick dark patches on a shaded patio are all living growth, not just dirt. That changes both how often to clean and how, because growth comes back fast if it is only blasted off rather than killed.
The schedule, surface by surface
| Surface | How often | Method |
|---|---|---|
| Vinyl or fiber-cement siding | Yearly; shaded walls may need it twice | Soft wash |
| Painted wood siding and trim | Yearly, gently | Soft wash; inspect paint as you go |
| Brick | Every one to two years, or when growth shows | Low to moderate pressure; avoid blasting mortar joints |
| Driveways, walks, patios | Once or twice a year | Pressure wash with a surface cleaner; pre-treat stains |
| Wood decks and fences | Yearly, ahead of sealing or staining | Low pressure with a wide tip, or a wood cleaner and rinse |
| Asphalt shingle roofs | When algae streaks appear, often every few years | Low-pressure chemical wash only |
| Gutters (exterior faces) | With the siding wash | Soft wash; clean the inside separately |
Timing through the Alabama year
Late spring, after the pollen
Pine and oak pollen coat everything from roughly March into April. Washing before it is over wastes the effort. Once pollen drops off, late April through May is the best window for the annual siding and concrete wash: warm enough for the cleaning solution to work, before the heat of summer.
Early fall
September and October are good for decks and fences, since the wood can dry in lower humidity and take a sealer before winter. It is also the time for a second concrete cleaning and for heavily shaded walls that greened up over the summer. For rentals and listings, a fall wash freshens curb appeal before the holiday market slows.
Avoid
Midday summer sun dries cleaning solutions on the surface before they work and scorches plants. Do not wash right before a hard freeze, because water in concrete pores and wood can freeze. And skip it right before heavy rain, which carries solution into beds and drains.
How much pressure each surface can take
These are typical working ranges used by exterior cleaners, not limits printed on a product. Always start lower and test in an inconspicuous spot.
- Concrete: commonly 2,500 to 3,500 PSI with a rotary surface cleaner, which cleans evenly and avoids the striped look a wand leaves.
- Wood decks and fences: commonly 500 to 1,200 PSI depending on the wood; softwoods like pine sit at the low end. Too much pressure raises the grain and leaves fuzzy, splintered boards.
- Siding and roofs: soft wash territory, usually under about 500 PSI at the surface. The cleaning solution does the work; the water just applies and rinses it.
Why "just blasting it" fails in humid climates
High pressure removes visible growth but leaves roots and spores in the surface texture, so mildew returns within weeks. On siding it also drives water behind panels into the wall, where it feeds the very mildew and rot you were trying to remove. Soft washing kills the growth, and it stays clean longer. Homeowners using a rented machine should treat it as a concrete tool and use a pump sprayer and a brush for everything else.
Fix what keeps it coming back
- Shade and airflow. Trim limbs and shrubs back from the house so walls dry after rain.
- Sprinklers. Heads that spray the siding or slab every morning grow algae on schedule. Re-aim them.
- Gutters and downspouts. Overflowing gutters stain siding and keep foundations and patios wet. Clean them and extend downspouts.
- Grading. Soil and mulch piled against siding keeps the bottom course damp; keep a gap.
If you do it yourself
- Respect the tip. A zero-degree tip at full pressure can cut skin and etch concrete. Use wide-angle tips and never point the wand at people, pets or your own feet.
- Stay off ladders with a wand. The recoil can pull you off balance. Use an extension wand or a downstream injector from the ground.
- Protect electrical fixtures. Keep spray off outlets, exterior lights, meters and the AC disconnect.
- Protect glass and screens. High pressure breaks window seals and tears screens.
- Mind the chemicals. Never mix bleach-based cleaners with ammonia or acids. Wear eye protection and gloves.
- Close windows and doors and cover nearby vehicles before you start.
- Test first. Try every new tip, distance and cleaning mix on a hidden spot, such as behind a shrub or under a deck, before working on anything visible.
Use the wash as an inspection
A clean house shows its problems: soft trim, peeling paint, caulk gaps, cracked siding, and concrete cracks that were hidden under grime. Walk it after washing and write down what you see. If the paint is chalking or bare, use the paint coverage calculator to estimate gallons before you get quotes.